Fix not propagating updating and propagating down the layout transition id if a subnode is added (#2018)

If a node was added to a supernode, the supernode could be in a layout pending state. All of the hierarchy state properties related to the transition need to be copied over as well as propagated down the subtree. This is especially important as with Implicit Hierarchy Management adding subnodes can happen while a transition is in fly

Author: maicki

AsyncDisplayKit/ASDisplayNode.mm

@@ -1877,18 +1877,35 @@ - (void)__setSupernode:(ASDisplayNode *)newSupernode
     }
     if (newSupernode) {
       [self enterHierarchyState:stateToEnterOrExit];
+      
+      // If a node was added to a supernode, the supernode could be in a layout pending state. All of the hierarchy state
+      // properties related to the transition need to be copied over as well as propagated down the subtree.
+      // This is especially important as with Implicit Hierarchy Management adding subnodes can happen while a transition
+      // is in fly
+      if (ASHierarchyStateIncludesLayoutPending(stateToEnterOrExit)) {
+        int32_t pendingTransitionId = newSupernode.pendingTransitionID;
+        if (pendingTransitionId != ASLayoutableContextInvalidTransitionID) {
+          {
+            ASDN::MutexLocker l(__instanceLock__);
+            _pendingTransitionID = pendingTransitionId;
+            
+            // Propagate down the new pending transition id
+            ASDisplayNodePerformBlockOnEverySubnode(self, ^(ASDisplayNode * _Nonnull node) {
+              node.pendingTransitionID = _pendingTransitionID;
+            });
+          }
+        }
+      }
+      
+      // Now that we have a supernode, propagate its traits to self.
+      ASEnvironmentStatePropagateDown(self, [newSupernode environmentTraitCollection]);
     } else {
       // If a node will be removed from the supernode it should go out from the layout pending state to remove all
       // layout pending state related properties on the node
       stateToEnterOrExit |= ASHierarchyStateLayoutPending;
 
       [self exitHierarchyState:stateToEnterOrExit];
     }
-    
-    // now that we have a supernode, propagate its traits to self.
-    if (newSupernode != nil) {
-      ASEnvironmentStatePropagateDown(self, [newSupernode environmentTraitCollection]);
-    }
   }
 }
 
@@ -2160,6 +2177,12 @@ - (void)setPendingTransitionID:(int32_t)pendingTransitionID
   ASDisplayNodeAssertTrue(_pendingTransitionID < pendingTransitionID);
   _pendingTransitionID = pendingTransitionID;
 }
+  
+- (int32_t)pendingTransitionID
+{
+  ASDN::MutexLocker l(__instanceLock__);
+  return _pendingTransitionID;
+}
 
 - (void)setPreferredFrameSize:(CGSize)preferredFrameSize
 {